This invention relates to an apparatus for measurement of the condition in a pressurized fluid and, in particular to such an apparatus adapted for measurement of absolute or differential pressure of a fluid medium and is particularly suited to pressure measurement of corrosive fluids. More specifically, this invention relates to a monocrystalline silicon chip, having a central diaphragm portion with integral semi-conductor strain gauges arranged in a Wheatstone bridge circuit for sensing, for example, pressure and a remote terminal portion for interconnections between the integral semi-conductor strain gauges and circuitry external to the chip. The chip is partially contained within a metal or plastic cartridge assembly, so that the diaphragm portion is situated within the central ported cavity of the cartridge assembly in communication with the fluid and the termination portion extends to the outside of the cartridge assembly. Since the remote terminal portion and associated interconnections to external circuitry are isolated from the fluid and therefore cannot be damaged or corroded under the influence thereof. The cartridge assembly is mounted within a housing assembly having fluid couplings for convenient connection with a source of pressurized fluid.
Silicon chip sensors, such as pressure sensors, have been long known in the art, but their general acceptance and usefulness in pressure sensing applications have been considerably restricted due to their incompatability with most working fluids. For example, in the prior art pressure sensor chips disclosed in U.S. Pat. No. 3,764,950 to Wallia; U.S. Pat. No. 3,820,401 to Louis; U.S. Pat. No. 3,930,412 to Mallon et al.; and U.S. Pat. No. 3,918,019 to Nunn, the connections between the chip and external circuitry for power and output signal sensing are subject to exposure to the pressurized fluid. Since these connections to external circuitry are conventionally made by ultrasonic or other bonding of fine aluminum or gold wire, typically having a diameter of 0.001 to 0.003 inches, to metallized pads which are fused to the chip, they are extremely vulnerable and fragile. In the prior art, these wires and metallized pads are fully exposed to the fluid whose pressure is being measured. This fluid may mechanically damage the delicate wires through hydraulic forces or corrode the wires and metallized pads through chemical action. Moreover, it is not uncommon for the fluids to be sufficiently conductive to provide electrical shorting paths between the wires and metal pads which degrade or nullify the pressure sensing circuitry. Attempts have been made in the prior art to coat the wires and chip surfaces with insulating organic materials or other coatings. These coatings are unsatisfactory, since they may damage the connections due to their high thermal coefficients of expansion or may themselves degrade due to high temperature. Such coatings may also negatively affect the sensitivity of the diaphragm portion of the silicon chip.